1. Field of the Invention
This invention relates generally to a synchronizing signal generator and, more particularly, is directed to a synchronizing signal generator which can produce various synchronizing signals used in a PAL-TV signal processing system.
2. Description of the Prior Art
In the color television (TV) signal of the PAL system, there is established the following relation among the frequency f.sub.sc of the color subcarrier signal, the horizontal synchronizing frequency f.sub.H and the vertical synchronizing frequency f.sub.V (=2/625 f.sub.H): EQU f.sub.sc =(284-1/4) f.sub.H +1/625 f.sub.H, or (1) EQU f.sub.sc =1135/4 f.sub.H +1/2f.sub.V ( 2)
the above relation (1) is established between the frequencies f.sub.sc, f.sub.H and f.sub.V so that, when the color subcarrier component is mixed into the luminance signal and bright and dark dots are produced on the screen of the picture tube, these dots are not conspicuous to a viewer.
By the way, if a reference oscillator with an oscillation frequency the same as the frequency f.sub.sc of the color subcarrier is provided and the oscillation output therefrom is frequency-divided, synchronizing signals having the above desired relation can not be obtained. More particularly, it is necessary that a signal of a frequency lower than the oscillation frequency f.sub.sc by 1/2 f.sub.V (=25Hz) be provided and then frequency-divided. Such a synchronizing signal forming circuit can not be made only of digital circuits. However, if an oscillator with an oscillation frequency which is the least common multiple of the denominator of formula (1) above is used as the reference oscillator, both the color subcarrier and the horizontal synchronizing signals can be produced by merely frequency-dividing the oscillation output from such oscillator. In such case, however, the oscillation frequency of the reference oscillator must be selected to be 11 GHz which is very high and can not be realized by present techniques.